The manufacture of timepieces, or musical boxes including a musical movement and/or a striking mechanism with complications, requires the use of mechanisms having an operating regularity of comparable quality to that of the timepiece movement in which they are contained, at least during the course of a musical or striking cycle where, although an unchanging duration in the cycle time is not sought, the rhythm imposed on the musical or striking sequence must imperatively be observed. Indeed, any defect is audible and unpleasant for the user, especially if the timepiece is an expensive one.
An energy source, generally formed by a strike barrel, generally supplies energy to raise one or several hammers to strike gongs, resonators, or bells, or even a sound box in the case of a musical box. The vibration of these gongs or suchlike is transmitted to the middle part, bezels and crystal of the timepiece, which radiate in the air. The energy is generally called for by a cam or toothed device, such as a simple or multiple strike wheel set, actuated by a lever or a trigger device controlled by the timepiece movement or by the user in the case of an alarm clock function or alarm. The amount of energy used for winding a hammer is very high in comparison to that necessary for the operation of the timepiece movement. Also the energy source of the striking mechanism, generally a barrel spring, has to be generously dimensioned to avoid the user having to wind or recharge too frequently, whether the energy source is mechanical, electrical or of another type.
The energy used by the striking mechanism is characterized by instantaneous peaks in consumption, which also influences the large size of the energy source, to ensure fatigue resistance.
Moreover, it is not unusual for the striking mechanism to experience racing, under the combined effect, on the one hand of the abrupt release of a large amount of energy broadly available in the energy source, and on the other hand of inertia. The consequences are detrimental, in particular as regards the nature of the following striking sequence, which may be incorrect. Or the following strike may not occur at the right time, which is more serious.
To prevent racing in pendulums and clocks, it is known to use a fly which brakes the rotation by air friction. These devices require space and cannot be properly integrated in watches.
Regulation of the striking tempo, or melody as appropriate, is achieved by a governor, which stabilises the let down speed of the barrel used for the strike, which may be the barrel of the movement, or a separate barrel, as is generally the case in pendulums.
The known governors for striking mechanisms are thus based on friction, or on shocks. They are often difficult to make, imprecise as regards speed, and very often noisy, which is unacceptable for an expensive musical or grand strike timepiece.
Any regulation of this speed, when it exists, is conventionally achieved with a lever system or with a mechanical governor with inertia blocks such as that disclosed in CH Patent No. 34 in the name of Barbezat-Baillot, which use a good deal of energy and may be bulky. Known governors are imprecise, and cannot precisely limit angular speed deviation.
The most compact is the lever governor, which is easy to make and adjust, using a simple stop pin. Generally, this type of governor operates at high speed, at around 100 to 150 oscillations per second, which results in 200 to 300 shocks per second. These shocks generate vibrations which are transmitted to the middle part, bezels and the crystal, which radiate in the air, like the chimes of the strike, with a noise that interferes with the sound of the chimes.
Further, these shock or friction based governors are difficult to make, imprecise as regards the regulated speed, and often noisy.
In short, in a timepiece including a striking mechanism or a musical box, and particularly in a musical watch or in a minute repeater watch, the variation in tempo is closely connected to the let down curve of the barrel spring. Consequently, in many cases, the chimes or music slow down at the end of the function, which is unpleasant for the user. Known governors require a good deal of space and/or are noisy.